SAW (surface acoustic wave) filters play a key role in telecommunications. For example, SAW filters are widely used as bandpass and spectrum-shaping filters in mobile and wireless applications. Other applications for SAW filters include wide area networks (WAN), wireless local area network (WLAN) communications, cordless phones, pagers and satellite communications. SAW filters are preferable to conventional LC filters as they are much smaller, cheaper and more versatile, making them ideal for telecommunication applications.
In SAW filters, electrical signals are converted to a mechanical wave in a device constructed of a piezoelectric crystal or ceramic. The wave is delayed as it propagates across the device, before being converted back to an electrical signal by other electrodes. More specifically, coupling between surface waves and electrical signals is achieved by interdigital transducers (IDTs). A simple form of the IDT consists of parallel fingers alternately connected to opposite electrodes to which the signal is applied.
For example, when an AC voltage is applied to input transducers, due to piezoelectricity, the transducer produces mechanical deformation of the piezoelectric substrate surface. This, in turn, results in a surface acoustic wave traveling on the surface of the piezoelectric substrate until reaching the output IDT, where it is transformed back to an electrical signal. When this wave reaches the output IDT, the electric field will induce a potential difference between neighboring electrodes such that the output IDT will convert the mechanical vibration into output voltages.
SAW filters can be designed to provide quite complex signal processing functions within a single package containing only a piezoelectric substrate with superimposed thin metal film input and output interdigital transducers (IDTs). SAW filters can be mass-produced using semiconductor microfabrication techniques, which enables reproducibility of the SAW filters. However, programming or tuning of the SAW filters has been found to be difficult to achieve.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.